The invention relates to motor vehicle driveshaft assemblies. More particularly, the invention applies to use of the mass distribution of a driveshaft tube to minimize the initial imbalance of a driveshaft assembly.
A drive train system transmits rotational power from the output of an engine/transmission assembly to the input of an axle assembly, through which the wheels of the vehicle are driven. To accomplish this, a typical vehicular drive train system includes a driveshaft assembly having first and second end fittings, tube yokes secured by welding to the opposite ends of a tubular shaft. The first yoke forms a portion of a first universal joint, which provides a rotatable driving connection between the output shaft of the engine/transmission assembly and a first end of the driveshaft assembly. Similarly, a second yoke forms a portion of a second universal joint, which provides a rotatable driving connection between the second end of the driveshaft assembly and the input shaft of the axle assembly. The universal joints accommodate a limited amount of angular misalignment between the axes of the driveshaft portions.
In some vehicles, the distance separating the engine/transmission assembly and the axle assembly is relatively short. For these vehicles, the driveshaft assembly is formed from a single, relatively long driveshaft tube having first and second yokes secured to the respective ends of the tube. In other vehicles, however, the distance separating the engine/transmission assembly and the axle assembly is relatively long, making it impractical to use a single driveshaft tube. For these vehicles, the driveshaft assembly is formed from separate, relatively short driveshaft sections. In a compound driveshaft assembly, a first end of the first driveshaft section is connected to the output shaft of the engine/transmission assembly by a first universal joint. A second end of the first driveshaft section is connected to a first end of the second driveshaft section by a second universal joint, and a second end of the second driveshaft section is connected to the input shaft of the axle assembly by a third universal joint.
The engine/transmission assembly induces a variety of relatively high frequency, lateral and torsional vibrations in the driveshaft assembly as it rotates in service. To avoid excessive vibration and noise in a driveshaft, the assembly is balanced, statically and/or dynamically, to determine the locations on the assembly where weights can be placed to avoid resonance, to attenuate noise, and to minimize flexural displacement.
Balance weights are conventionally attached to the external surface of a driveshaft tube by welding or with adhesives. However, heat produced by the welding process can structurally affect the driveshaft tube. Alternatively, balance weights are attached to the interior surfaces of the driveshaft tube so the weight is retained in position against the tendency of centrifugal force and flexural displacement of the driveshaft to dislodge the weight. It is preferable to attach a balance weight to the interior of a driveshaft after the unit is assembled, rotated, and its balance tested to determine the location where balance weight could be placed to improve performance, especially its response to vibratory excitation. However, access to the interior of an assembled driveshaft is limited. Securing a balance weight internally at an optimal angular position about the longitudinal axis of the assembly is difficult without disassembling the driveshaft. Disassembly, installation of the weight, and reassembly is time consuming and adds cost.